1. Field of the Invention
The present invention relates to wireless terminals and wireless communication methods, and more particularly, to a wireless terminal constituting an ad-hoc network to perform communication and a wireless communication method for the wireless terminal.
2. Description of the Related Art
In recent years, ad-hoc network has been watched as one of infrastructures for ubiquitous network society. Ad-hoc network requires no access points, and data is exchanged across a network constituted by wireless terminals connected to one another, such as notebook computers, PDAs, and mobile telephones.
In conventional ad-hoc networks, highly reliable connection-oriented communication is carried out using response frames. Specifically, on receiving a frame, the receiving wireless terminal sends a response frame back to the wireless terminal which transmitted the frame, whereupon the transmitting wireless terminal recognizes that the frame has been normally communicated to the succeeding wireless terminal.
FIG. 15 illustrates the radio coverage areas of wireless terminals. Three wireless terminals 131 to 133 are positioned as illustrated in the figure. A radio coverage area 141 indicates an area where radio waves from the wireless terminal 131 can reach. Accordingly, radio waves from the wireless terminal 131 reach the wireless terminal 132. A radio coverage area 142 indicates an area where radio waves from the wireless terminal 132 can reach, and thus radio waves from the wireless terminal 132 reach the wireless terminals 131 and 133. A radio coverage area 143 indicates an area where radio waves from the wireless terminal 133 can reach; therefore, radio waves from the wireless terminal 133 reach the wireless terminal 132.
In FIG. 15, suppose the case where data is transmitted from the wireless terminal 131 to the wireless terminal 133. Since radio waves from the wireless terminal 131 do not reach the wireless terminal 133, data needs to be relayed by the wireless terminal 132. Specifically, the wireless terminal 131 first transmits a frame (data) to the wireless terminal 132, which then transmits the received frame to the wireless terminal 133.
FIG. 16 is a sequence diagram illustrating operations of the wireless terminals shown in FIG. 15. As in the above example, the wireless terminal 131 transmits data to the wireless terminal 133. In this case, in Step S101, the wireless terminal 131 transmits a frame to the wireless terminal 132. In Step S102, the wireless terminal 132 sends a response frame indicative of reception of the frame back to the wireless terminal 131. Then, in Step S103, the wireless terminal 132 transmits the frame received from the wireless terminal 131 to the wireless terminal 133. In Step S104, the wireless terminal 133 sends a response frame indicative of reception of the frame back to the wireless terminal 132. In this manner, data is successively relayed by the wireless terminals up to the last (destination) wireless terminal in a manner such that each receiving wireless terminal sends a response frame back to the transmitting wireless terminal, thereby achieving highly reliable connection-oriented communication.
Meanwhile, there has been proposed a routing method for establishing an optimal path between a transmission origin node and a destination node in an ad-hoc network (see, e.g., Unexamined Japanese Patent Publication No. 2004-48478 (paragraph nos. [0011] to [0018], FIG. 1)).
In the conventional wireless terminal, however, a response frame has to be sent back to the wireless terminal from which data has been received, with the result that the data transfer efficiency lowers by an amount corresponding to the time required to transmit and receive the response frame. A problem also arises in that traffic increases because of response frames.